The air delivery controls are divided into two primary areas. The first, air speed, is dependent upon blower motor speed. The second, air distribution, is related to various single or multiple air outlets.

The blower motor forces ambient air into the vehicle's interior. The vehicle operator determines the blower motor's speed by toggling the blower motor switch manually or by using the automatic mode The blower motor will always operate at some speed as long as the HVAC control module is in any position other than OFF, as long as the ignition switch is in the RUN position.

Power is provided to the blower motor from the battery positive voltage circuit. Ground is provided by the ground circuit.

When a blower speed is selected manually, a signal is sent from the HVAC control module to the HVAC control processor on the class 2 serial data circuit. Once the signal is either received by the HVAC control processor or an automatic blower speed is determined by the processor, a signal is sent to the blower motor on the blower motor speed control circuit. The blower motor will then pulse width modulate (PWM) the ground. When a low blower speed is requested, the PWM signal is reduced. When a higher blower speed is requested, the PWM signal is increased. In automatic operation, the HVAC control processor will determine what blower speed is necessary in order to achieve or maintain a desired temperature. Toggling the blower switch manually also activates the VF display for the blower speed selected. Whenever you service the blower motor, carefully handle the motor. The balance of the blower motor is very sensitive to handling.

When the vehicle operator toggles the blower motor switch, the blower can operate in either a manual, automatic or combination of the two modes. When the blower motor switch is toggled up one position, from the AUTO mode, the blower motor speed increases slightly and the HVAC control module displays HI AUTO. The fan operates automatically, similar to the automatic setting, except at a slightly faster blower speed.

When the blower motor switch is toggled up two positions, from the AUTO mode, the blower motor runs at a fixed speed and the HVAC control module displays HI. This is a complete override of the automatic blower system.

When the blower motor switch is toggled down one position, from the AUTO mode, the blower motor speed decreases slightly and the HVAC control module displays LO AUTO. The fan operates automatically, similar to the automatic setting, except at a slightly slower blower speed.

When the blower motor switch is toggled down two positions, from the AUTO mode, the blower motor runs at a fixed speed and the HVAC control module displays LO. This is a complete override of the automatic blower system.

Off Mode

When the vehicle is moving, air flowing over the vehicle increases the air pressure just ahead of the windshield. This forces air into the ambient air inlet, into the HVAC module and out through the floor outlets. The HVAC control processor attempts to match the inside air temperature and driver selected temperatures. Since the A/C compressor is not running, the incoming air may be warmed but not cooled. Press the OFF switch to turn off the HVAC system. The ambient air temperature will show on the VF display at all times. The HVAC control module will return to the previous driver settings, except for manual RECIRCULATION and FRONT DEFROST.

Recirculation Mode

When the recirculation mode is requested, whether manual or automatic, a solenoid inside the vacuum control assembly connects the recirculation actuator to the vacuum source. Power is provided to the recirculation solenoid by the vacuum control assembly supply voltage circuit. Ground is provided internally within the HVAC control processor. When the solenoid is grounded, vacuum is supplied to the recirculation actuator. The recirculation actuator retracts, closing the recirculation door. This draws air from inside the vehicle instead of fresh air from the outside.

The recirculation mode can be used in both manual and automatic operation. Recirculation is only allowed in the following modes:

The RECIRC LED will flash to alert the driver that recirculation mode is not available. When in automatic mode, recirculation will stay on until either the vehicle operator selects ambient air or the automatic system has cooled the vehicle sufficiently. The recirculation function will operate for the entire ignition cycle. Pressing the recirculation switch with the system off, will return the system to the last setting prior to the system being turned off.

Automatic Modes

The automatic HVAC system will warm up/cool down and maintain the interior temperature of the vehicle by controlling the A/C compressor clutch, blower motor, air temperature, vacuum and recirculation actuators to achieve the desired temperature. For fully automatic operation, both the blower and mode switches must be in the AUTO position. Blower speeds will change automatically based on inputs to the HVAC control processor. The HVAC control module will always come back to the last settings after an ignition cycle or, if equipped, to the last settings of the driver by pressing the UNLOCK button on the remote keyless entry fob and placing the ignition in RUN. Only FRONT DEFROST and manual RECIRCULATION will have to be reset after each ignition cycle.

Moisture tends to accumulate in the HVAC module assembly after the engine has been shut off. The HVAC control processor will purge the HVAC module of stale air and moisture to prevent window fogging. The blower motor is delayed until the engine coolant temperature reaches 36°C (97°F) or the program number would result in cooling. If neither of these conditions exists within approximately 1-4 minutes (depending upon ambient temperatures), the HVAC control processor automatically resumes normal operation. The HVAC control processor will move to the floor mode and run the low blower to purge out the air and moisture. Purge mode can be bypassed if any manual modes are selected.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. On cold engine start-up, low blower speed will be selected and airflow will be directed on the windshield. This is done to prevent windshield fogging. The normal operation resumes after the engine coolant temperature reaches 36°C (97°F) or the program number would result in cooling. If neither of these conditions exists within approximately 1-4 minutes (depending upon ambient temperatures), the HVAC control processor automatically resumes normal operation. To warm the interior quickly, maximum heat mode is used where the blower is at maximum speed, floor mode, air temperature actuator is in full hot and ambient air is being drawn in. The vehicle operator can select the extreme warm setting of 32°C (90°F), but the system will not warm the vehicle any faster or regulate the blower speed. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control processor.

In warm temperatures, the automatic HVAC system will provide A/C in the most efficient manner. On vehicle start up, the HVAC control module will monitor for conditions that indicate the possible presence of moisture in the HVAC module. To avoid blowing hot air and moisture out at the driver, the HVAC control module moves the mode door toward the floor and runs the medium speed blower for 4 seconds. This purge mode can be bypassed if any manual mode is chosen or if the blower was left on HI speed before turning off the vehicle. To cool the interior quickly, maximum cool mode is used where the blower is at maximum speed, air temperature actuator is in full cold and the recirculation actuator is drawing air from inside the vehicle. The vehicle operator can select the extreme cool setting of 16°C (60°F), but the system will not cool the vehicle any faster or regulate the blower speed. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.

Steering Wheel Blower Motor Switch

A separate blower motor switch is mounted on the steering wheel to allow the driver to adjust the blower speeds. Power to the steering wheel control switch is delivered from the rear fuse block, through the steering column fuse holder, and inflatable restraint steering wheel module coil on the battery positive voltage circuit. When the driver toggles the blower switch up or down, the voltage is sent through a series of resistors. That varied voltage is sent back through the inflatable restraint steering wheel module coil to the instrument cluster through the remote radio control circuit. Once the instrument cluster receives the varied voltage signal, the information is sent out over the class 2 serial data to the HVAC control processor where the blower speed is adjusted.

Auxiliary Blower Motor Switch

The auxiliary blower motor provides additional airflow for the back seat passengers. The auxiliary blower motor operates independently from the HVAC control processor. Passengers can operate the system in manual mode only. The only time the auxiliary blower motor is not available is when the HVAC control module is in FRONT DEFROST.

Power is provided to the auxiliary blower motor from the rear fuse block. The ground circuit provides a ground for the auxiliary blower motor switch and auxiliary blower motor resistor. Depending upon selected blower speeds, voltage is either supplied directly to the blower motor or voltage is varied by a series of in-line resistors on the ground side of the circuit.

Auxiliary Low Blower Speed

When the auxiliary blower switch is in any position other than OFF, residual airflow from the front blower motor will flow from the auxiliary HVAC system.

When the Low blower speed is selected, the auxiliary blower motor switch applies a ground for the auxiliary blower motor. Voltage is routed from the auxiliary blower motor, through the high blower motor control circuit, through 3 series resistors in the auxiliary blower motor resistor assembly to achieve the desired auxiliary blower speed. The circuit is grounded by the low blower motor control circuit, auxiliary blower motor switch and ground circuit.

Auxiliary Medium Blower Speeds

When the Medium blower speed is selected, the auxiliary blower motor switch applies a ground for the auxiliary blower motor. Voltage is routed from the auxiliary blower motor, through the high blower motor control circuit, through 2 series resistors in the auxiliary blower motor resistor assembly to achieve the desired auxiliary blower speed. The circuit is grounded by the medium 1 blower motor control circuit, auxiliary blower motor switch and ground circuit.

When the Medium High blower speed is selected, the auxiliary blower motor switch applies a ground for the auxiliary blower motor. Voltage is routed from the auxiliary blower motor, through the high blower motor control circuit, through a resistor in the auxiliary blower motor resistor assembly to achieve the desired auxiliary blower speed. The circuit is grounded by the medium 2 blower motor control circuit, auxiliary blower motor switch and ground circuit.

Auxiliary High Blower Speed

When the High blower speed is selected, the auxiliary blower motor switch applies a ground for the auxiliary blower motor. Voltage is routed from the auxiliary blower motor, through the high blower motor control circuit, to achieve the desired auxiliary blower speed. The circuit is grounded by the high blower motor control circuit, auxiliary blower motor switch and ground circuit. The HVAC control processor monitors the high blower speed on the high blower motor control circuit.

When the mode switch is pressed, a signal is sent from the HVAC control processor to the vacuum control assembly. The HVAC control processor will provide ground for the necessary mode actuator solenoid, connecting the desired mode actuator to vacuum. The HVAC control processor provides power to the vacuum control assembly through the vacuum control assembly supply voltage circuit. Ground is provided by the HVAC control module.

Mode Switch

Use the MODE switch in order to change the air delivery mode in the vehicle. Toggling the MODE switch when in AUTO mode will lock in the air flow mode that AUTO was controlling. The system will stay in that mode until the MODE or AUTO switch is pressed. Pressing the MODE switch also activates the digital display for the mode selected. If an airflow mode is currently displayed, pressing the MODE switch selects the next air flow mode. The air flow direction will sequence through the following modes:

Mix-Blend Mode

When the driver selects the MIX-BLEND mode, air delivery is divided between the floor and windshield outlets. The A/C compressor is activated if ambient air temperatures are above 3°C (38°F). The defroster door is closed and ambient air is drawn in.

Floor Mode

When the driver selects the FLOOR mode, air is delivered through the floor outlets with some toward the windshield and side vents. Vacuum is applied to the mode actuator through the Yellow vacuum line. The mode actuator will retract, opening the Heater Door.

Bi-Level Mode

When Bi--Level is selected, air is delivered through the instrument panel outlets and to the floor outlets. Vacuum is applied to the mode actuator through the Red and the Yellow vacuum lines, and to the defrost actuator through the Blue vacuum line. Applying vacuum to both sides of the Mode actuator will hold the Mode Door stationary in the half open position. The Defroster actuator will retract, closing the Defroster Door and opening the Vent Door.

Vent Mode

When VENT is selected, air is delivered through the instrument panel outlets with a small amount of air delivered to the floor. Vacuum is applied to the mode actuator through the Red vacuum line, and to the Defrost actuator through the Blue vacuum line. The Mode actuator will retract, closing the Heat Door. The Defroster actuator will retract, closing the Defroster Door and opening the Vent Door.

Front Defrost Mode

The front defrost mode is the only setting that is not controlled by the automatic HVAC system. When FRONT DEFROST is selected, the A/C compressor is activated and ambient air is brought into the vehicle. The blower motor will be activated and air will be directed toward the windshield with a small amount of air toward the side window outlets. Vacuum is applied to the mode actuator through the red vacuum line. The mode actuator will retract, closing the heater door through mechanical linkage. Pressing the AUTO or OFF button will turn off front defrost mode. Recirculation mode is not available in front defrost. The rear window defogger does not affect the HVAC system at all.

Outside Air Mode

When the OUTSIDE AIR switch is toggled, ambient air is brought into the vehicle. This mode has no effect on the system when FRONT DEFROST mode is selected. OUTSIDE AIR and RECIRCULATION are separate modes and are not available together. When OUTSIDE AIR is selected, when in automatic mode, the HVAC system will stay in this mode until AUTO is pressed again.

Dual Zone Control Switch

The right air temperature switch is provided to allow the passenger to offset air discharge temperatures on the right side of the vehicle. Passenger temperatures can be offset 2°C (4°F) cooler or warmer than the primary setting. The temperature switches operate independently from each other. To activate the dual zone, the passenger toggles the right air temperature switch to the desired offset. A signal is sent from the HVAC control processor to the right air temperature actuator on the passenger HVAC control assembly circuit. The passenger side temperature will appear on the VF display as a red and blue bar graph. Temperature offset will be allowed as long as the driver set temperature is not in maximum hot or cold. If the right air temperature switch has been turned on, it can be turned off by pressing the right air temperature switch. Greater sunload on one side of the vehicle may cause the discharge air temperatures to be different, even when the HVAC system is not operating in a dual zone mode.

The HVAC control processor provides power to the right air temperature actuator through the off/run voltage circuit. Ground is provided by the low reference circuit.

The right air temperature actuator is an electronic stepper motor with feedback potentiometers. 0 volts drives the actuator in one direction while 5 volts moves the actuator in the opposite direction. When the actuator receives 2.5 volts, actuator rotation stops. A 5-volt reference signal is sent out over the 5-volt reference circuit, from the HVAC control processor, to the right air temperature actuator. When a desired temperature offset is selected, whether manual or automatic, the solid state circuit is used to determine the right air temperature door position signals value. A separate 5-volt reference is sent from the HVAC control processor to the solid state circuit. The HVAC control processor software uses this reference voltage to determine the right air temperature actuators position through the right air temperature door position signal circuit. The motor moves the right air temperature actuator door to the desired position.